Effect of porosity on dielectric properties of ZnO ceramics

Abstract

In this study we investigated the effect of porosity level on the dielectric properties and conductivity of ZnO ceramic samples sintered by pressure-less solid-state reaction method. The relative permittivity ( r ) and, tangent loss value decreased gradually with increasing porosity, being 1.9 × 105 and 35.6 × 103 for sample with low porosity and high porosity level, respectively at room temperature. Also the tangent loss decreases with increasing porosity level being quite high (∼102 ) at low frequencies and, low (∼10−1) at high frequencies. The complex part of the relative permittivity results could be fitted to the Maxwell-Wagner (MW) model suggesting a poly-dispersive relaxation time. The frequency dependence-ac conductivity determined by means of dielectric data was strongly dependent of the porosity level. It decreases sharply with increasing porosity level is frequency independent- up to ∼104 − 105 Hz followed by an abrupt increase at higher frequencies. These data were discussed in terms ZnO defects such as Zn interstitial and oxygen vacancies present in the grain boundaries.